1. Field of the Invention
The present invention relates to a double wall pipe with an inner high pressure pipe having as inner flow space for harmful and/or flammable liquids, particularly fuel to be injected or hydraulic oil, and with an outer protection pipe coaxially arranged around the inner pipe, having an outer flow space between inner pipe and outer pipe, for possibly leaking or spilling liquid from the inner pipe.
2. Description of Related Art
Industrial steel pipes, widen carry harmful and/or flammable liquids such as fuel, hydraulic oil, acid or others need to have an outer protection as a means of spill prevention. This type of spill prevention is compulsory for main and auxiliary engines on ships required by SOLAS, international convention for the safety of life at sea, regulations. Today standard is to use flexible hoses or simple pipes that cover the pressure-carrying pipe. We are talking about two separated pipes, or pipe and hose drat are carrying out this requirement.
Flexible hoses are usually ruled with complex distance holders. Such distance holders have only limited life lime caused by different vibrations of these two components. For this reason, after not specified time the protection hose gets in touch whit the pressure pipe and starts to cause mechanical damages. The solution of using normal steel pipes as a protection tube causes the same problems of not defined touching surfaces between the components because of bending the pipe during the manufacturing process. Contact corrosion can damage both pipes. Resuming these details a can be stated, that up to now two components are necessary to fulfill the requests of a double wall pipe in order in have any effective spill prevention on pressure carrying pipes.
Especially in the field of large combustion engines used as main or auxiliary engines of ships or in power plants for production of heat and/or electricity, it is known to arrange the fuel pipes of a diesel engine inside another pipe shell in order to keep possible leakage inside the outer shell. In the case of a leakage, the leaking fuel may be carried along inside the outer shell away from the vicinity of the engine. Such in arrangement with a double wall fuel pipe system is described in the European patent application EP 1 150 006 A2.
Further in the U.S. Pat. No. 6,286,536 B1 a high pressure fuel injection pipe for diesel engines with an outer protection pipe in a special, embodiment is disclosed in order to prevent scatter and leakage of a fuel outside the engine. Nevertheless the protection pipe has an inner diameter a little greater than the outer diameter of the injection pipe, so the two tubes are not counseled with each other over section. The vibrations from the engine cause different oscillations of the not uniform parts of the double wall fuel pipe.
Especially for fuel injection pipes for two stroke diesel engines considerable fuel volumes are injected under high pressure through the injectors into the cylinder. Thereby the reciprocating loads from nearly atmospheric pressure to high injection pressure up to 700 bar, the surrounding and frictionally induced heat within and around the fuel pipe up to 100° C. require high quality tubes which are sensitive to damages. Thus undefined different vibrations, undefined touching surfaces and other irregularities can damage both pipes.
Therefore, an object of the invention is to improve the life time of double wall pipes and decrease production costs.